Heat olive oil in a large saucepan over medium heat. Add the onions and garlic and sauté until soft but not browned, 3 -4 minutes.
Put the tomatoes along with the sauce and chipotles in a blender and puree. Add to the onions and garlic along with the rest of the ingredients and simmer for about 30 minutes stirring occasionally.
Puree the barbeque sauce in a blender in batches until smooth. Remember to remove the little plastic top to the blender lid so it does not explode on you. Strain into a bowl pushing the sauce through a sieve to remove any solids and let come to room temperature. Transfer to a jar or airtight container. Can be stored for up to a week in the fridge.
Notes
Lea & Perrins Worcestershire sauce is gluten-free in the United States but possibly not in England or the British Isles. If you are concerned, just leave it out.